An ongoing problem in the design of ventilating systems for the internal spaces of headlamps is that it is necessary to ensure that air which may contain humidity to a greater or lesser extent, and which may have penetrated into the headlamp, is able to be properly evacuated according to the differential pressures that may exist, while at the same time avoiding any penetration of foreign matter such as water, mud, etc. into the interior of the headlamp.
It is accordingly known to provide a headlamp housing with a system of chicanes, labyrinths or similar which enable air to flow while preventing penetration of foreign matter.
It is also quite conventional, as disclosed in particular in the specification of French published Patent Application FR2212794A, to locate the ventilation orifice in a part of the lamp which may for example be cylindrical, and which may project outwardly from the casing or housing of the lamp, the projecting part being closed at its free end by means of a cap. The air passes from the interior of the headlamp to this free end, and then from the latter it passes once again towards the headlamp casing, the passage through which the air flows being brought in communication with the outside in a suitable way.
This known type of ventilation orifice does however have a certain number of drawbacks. First of all it does not perfectly satisfy the requirements mentioned above, in particular when the headlamp is directly exposed to a water jet from a high pressure washing apparatus or the like. This is due, especially, to the particular configuration followed by the ventilation path described above. In addition, the quality of sealing between the cap and the end of the cylindrical projection, which is critical in the avoidance of any penetration of mud, may deteriorate with time. Indeed, the cap may even become completely separated from the casing, and this may lead to substantial penetration of foreign matter into the inside of the headlamp.